Jeong Yak Yong is a historical drama about a secret royal inspector, Jeong Yak Yong (Park Jae Jeong). He carries out his job righteously, so King Jung Jo trusts him. However, Yak Yong is blamed by people who are jealous of him and finally gets demoted to the low-ranking government position of the Chalbang official of the Geumjeong area. He doesn't expect a lot of work in his new position, but cases occur everywhere for the Sherlock Holmes of his time period.